This invention relates generally to electronic components and more particularly concerns low profile surface mountable inductive components having a structure that improves the manufacturability and performance of the component.
The electronics industry provides a variety of wire wound components such as inductors which come in a variety of package types and configurations. For example, inductors may be provided in through-hole or surface mount package configurations. In addition, some inductors are provided with a base structure, such as a plastic header, having an internal opening through which a core, such as a drum or bobbin type core, is disposed and mounted.
Although many advances have been made with respect to the packaging and structural arrangements of wire wound components, most (if not all) of the available components continue to use traditional gluing or potting methods to attach the various pieces of the component, (e.g., core, base, etc.), to one another. More particularly, the core and base structures of existing open base wire wound inductive components are typically connected by attaching the core to the base at the edges of the core. For example, with respect to existing coil components having bobbin type cores, the core and base are normally attached by connecting at least one of the flanged ends of the bobbin core to the base. Such methods and configurations for attaching the pieces of wire wound components are problematic for a variety of reasons.
One problem associated with the use of existing gluing or potting methods to attach the pieces of a wire wound component (or coil component) is the inability of the adhesive to withstand the harsh conditions the component is exposed to during its production and use. For example, surface mount components are attached to a printed circuit board (PCB) via solder paste, which requires the PCB and component to be passed through a solder reflow oven at temperatures high enough to briefly melt the solder paste and heat the leads or terminals of the component and corresponding lands on the PCB so that the solder can electrically connect the component to the lands or traces on the PCB. Similarly, through-hole components are connected to PCBs by placing the leads or terminals of the component through holes in the PCB and then passing the PCB and the component through a solder bath (or solder wave) which is run at temperatures high enough to heat the leads of the component and lands on the PCB so that the solder can electrically connect the component to the lands on the PCB. Unfortunately, most adhesives become rigid when subjected to such high temperatures and lose their flexibility which can cause the wire wound component to fail specified vibration parameters, as will be discussed further below.
In addition to the high temperatures encountered during the placement of the component on a PCB, the adhesive must also be able to withstand wide ranges of temperatures and other environmental conditions the component will be subjected to during its lifetime. For example, in automotive applications, the component may be subjected to, and must withstand, a range of temperatures, (e.g., −40° C. to +150° C.), and the associated thermal stresses that accompany such temperatures. Thus, the adhesives used must allow the pieces of the component to move to account for such things as thermal expansion and contraction of the materials used in each component, thermal shock, thermal cycling, and the like. As mentioned above, most adhesives become rigid when subjected to such temperature ranges and lose some flexibility. Often times, this reduction in the flexibility of the adhesive can lead to the pieces of the component damaging one another when movement occurs due to thermal expansion and contraction.
In addition to the wide range of temperatures and associated movements, the component must also withstand additional stresses and environmental tests such as mechanical shock and mechanical vibration. For example, during product validation the component may be subjected to various shock and vibration tests which require the adhesive to withstand movements of the pieces of the component such as axial movement of the core with respect to the base. These stresses and conditions often prove too demanding for traditional adhesives. For example, in components having bobbin cores glued to base structures at the edges of the flanged end of the bobbin core, the glue often provides too much or too little axial movement of the bobbin with respect to the base. More particularly, since the bobbin is inherently weaker in axial flexure at the edges of the flanged ends it often does not allow for the desired axial movement when connected about the edges, thereby increasing the risk of component damage such as cracking and/or component failure. In other instances, the connection between the bobbin and the base may provide too much axial movement between the core and base. This too can increase the risk of component damage to either the core or base. The glue also adds weight which must be born by the base and core during mechanical shock and vibration testing. The extra mass load of the glue on the base and core, and the failure of distributing this mass over a larger portion of the base and core, often can lead to damage and failure of the component during vibration and mechanical shock validation.
Another problem associated with use of adhesives in coil components is the inability of the adhesive to be applied to small parts in a uniform and efficient manner. In addition, existing gluing or potting methods are labor intensive and difficult to automate. Often times, the manual and automatic processes used to apply the glue leave glue on the top and bottom surfaces of the bobbin which disrupts these otherwise planar surfaces of the component and may make the component rest unevenly on a PCB or make the component difficult or impossible to pick up and place with industry standard pick-and-place machinery. For example, excess glue on the bottom surface of the component (e.g., bobbin, legs or base), may alter the height of the component which can make the component unacceptable for various low profile component applications such as PCMCIA cards, laptop computers, PDAs, mobile telephones, and the like. In another example, excess glue on the upper surface of the component (e.g., bobbin or base) can prevent the vacuum tip of a pick-and-place machine from establishing sufficient suction force to lift the component out of its reel and tape packaging so that it can be placed on the PCB.
Traditional gluing methods may also result in the glue leaking out between the bobbin and base leaving little or no glue at the edges of the bobbin flange and base. Such instances result in weak or missing connections between the pieces of the component and increase the likelihood of component, or circuit, failure during testing. The glue may also overflow the sides of the base which can result in an unacceptable condition. For example, in densely populated circuits where component footprints and size are critical features, hardened glue extending from the side of a component may prevent the component from being packaged within its tape and reel compartment, or from being accurately positioned on the corresponding lands of the PCB due to the glue contacting other components or structures on the circuit, or from being placed on the circuit at all due to an inability to clear other components or structures.
Accordingly, it has been determined that the need exists for an improved wire wound component and method for manufacturing same which overcome the aforementioned limitations and which further provide capabilities, features and functions, not available in current devices and methods for manufacturing.